Article Series

  1. Vitamin D - The Sunshine Vitamin
  2. Vitamin D Requirement Per Day
  3. Vitamin D Deficiency

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Vitamin D Deficiency

Vitamin D Deficiency
Table Of Contents
  1. Risk Groups
  2. Causes of Vitamin D Deficiency
  3. Symptoms of Vitamin D Deficiency
  4. Consequences of Vitamin D Deficiency
  5. Recognizing and Detecting Vitamin D Deficiency
  6. Treatment for Vitamin D Deficiency
  7. Preventive Measures

Vitamin D is primarily needed for the mineral metabolism of calcium and phosphorus. Through its hormone-like effect, it enables the absorption and processing of these two nutrients. Thus, Vitamin D indirectly contributes to strong bones or bone hardness.

A Vitamin D deficiency is a global problem in all age groups. 1 2 3 4. It is estimated that approximately one billion people have low vitamin D blood levels. 5.

Risk Groups

The risk groups for vitamin D deficiency include 6 7 8:

  • Pregnant and breastfeeding mothers and their infants
  • People with liver and kidney diseases
  • Elderly individuals
  • Obese individuals
  • Dark-skinned individuals
  • People who spend time indoors, predominantly use sunscreen, and cover their arms and legs
  • Vegans

Multiple studies also show that vegans have reduced vitamin D levels (serum 25-hydroxyvitamin D3) 9 10 11 12 13.

Causes of Vitamin D Deficiency

The main cause of vitamin D deficiency is insufficient exposure of the skin to sunlight. 90% of our vitamin D is produced through direct sunlight. The remaining 10% is obtained through food. In order to produce vitamin D, the ultraviolet light present in sunlight is needed, and it is converted into vitamin D with the help of precursors from food and cholesterol. If vitamin D stores are not adequately replenished during the summer months, deficiency symptoms can occur as early as the first days of winter. In winter months, vitamin D cannot be formed through the skin in some latitudes. In certain regions, the necessary UVB rays for vitamin D production are not available during the winter months as they are absorbed by the atmosphere. At latitudes of 52°N and higher (i.e., further north), no vitamin D can be produced from October to March 14. Further south, up to 42.2°N, vitamin D synthesis through UVB sunlight is not possible from November to February. In winter months, vitamin D can only be produced from 34°N and further south. Studies show that vitamin D levels are also low in Northern Europe during the winter months 15.

Using sunscreen also reduces the impact of UVB on the skin, which can lead to deficiency despite spending numerous hours in the sun. Sunscreen with a sun protection factor (SPF) of 8 or higher completely inhibits the synthesis of vitamin D in the skin 16.

Since vitamin D can be synthesized through the skin with the help of sunlight, people who lack the exposure of sunlight on the skin can also experience a deficiency. For example, indoor athletes are more prone to deficiency compared to athletes who train outdoors 17 18.

Individuals with a darker skin type require more time in the sun for vitamin D synthesis through the skin compared to fair-skinned individuals, as melanin (brown and black pigments) acts as a natural sunscreen 19.

Another cause can be the inadequate intake of foods rich in vitamin D. Except for mushrooms, unprocessed plant-based foods do not contain vitamin D.

Even a fat digestion disorder or intestinal disease (e.g., short bowel syndrome) can be the cause of a vitamin D deficiency, which disrupts the absorption from food (malabsorption) 20.

Obesity, as mentioned earlier under risk groups, is associated with a vitamin D deficiency. Since vitamin D is fat-soluble, it is quickly stored in the fatty tissue of obese individuals 21. Furthermore, obesity hinders the release of vitamin D into the blood 22. Even a 10% higher BMI leads to a four percent reduction in 25-hydroxyvitamin D, the storage form of vitamin D 23.

As you age, your body's synthesis of vitamin D decreases because the concentrations of vitamin D precursors in the skin decrease 24. Therefore, it is particularly important to ensure an adequate intake of vitamin D from the age of 65+.

If the kidneys are chronically weakened (renal insufficiency), it can lead to a disruption in the formation of calcitriol, which is responsible for the numerous functions of vitamin D in the body.

Additionally, a magnesium deficiency may contribute to a vitamin D deficiency 25 26. This shows that a high intake of magnesium through diet or supplementation can significantly reduce the occurrence of vitamin D deficiency 27 28. Foods containing magnesium can be found here.

Smokers also have lower blood levels of vitamin D.

Other causes of vitamin D deficiency can include 29 30:

  • Pancreatic disorders (e.g., pancreatic insufficiency)
  • Skin conditions like psoriasis
  • Air pollution
  • Lactose intolerance

Symptoms of Vitamin D Deficiency

A deficiency in vitamin D can lead to the following symptoms, among others: 31 32:

  • Bone deformities (e.g., bow legs)
  • Bone pain 33
  • Knee pain
  • Back pain 34 35
  • Joint pain
  • Headaches
  • Poor mood, depression, and fatigue, as well as sleep disturbances 36 37 38 39 40
  • Tooth Decay / Periodontitis
  • Increased susceptibility to respiratory infections 41
  • Skin problems (such as atopic dermatitis, psoriasis, vitiligo, acne, and rosacea)
  • Hair loss / Alopecia Areata 42 43 44 45
  • poor wound healing 46 47

A deficiency may also lead to impaired muscle function, muscle pain, muscle weakness, especially in adults and older individuals 48 49 50 51. The muscle pain is presumed to be due to vitamin D pain receptors (nociceptors) in the nerve cells that make the pain perceptible 52.

Note: All mentioned symptoms can also have other causes and are not necessarily attributable to a vitamin D deficiency.

Consequences of Vitamin D Deficiency

A lack of vitamin D can lead to rickets (increased softness of the bones/bone deformities) in childhood and, particularly in advanced age with reduced bone density, to osteopenia, later osteoporosis, and osteomalacia 53 54 55. The reason for this is that vitamin D is needed for the absorption of calcium from the diet. When vitamin D levels are low in the body, less calcium is absorbed. Parathyroid hormone is released and activates the release of calcium from the bones (hyperparathyroidism) to ensure an adequate supply of calcium for other bodily functions such as heartbeat, nerve conduction, and muscle contraction. The release of calcium leads to porous bones, faster aging, and an increased risk of fractures.

A vitamin D deficiency during pregnancy can have negative effects on the development of the unborn child. Maternal vitamin D deficiency can be a risk factor for preeclampsia, infections, and bacterial vaginosis 56 57. In addition, the children in adulthood as well as the subsequent generation may be more susceptible to diseases 58. Scientists conducting a meta-analysis, which combined 20 studies with 9,209 participants, identified a consistent link between vitamin D deficiency and an increased risk of gestational diabetes 59. Additionally, low serum levels of vitamin D are associated with type 1 diabetes in children 60.

Furthermore, a connection between vitamin D, dementia, and Alzheimer's has been established. Individuals who did not sufficiently meet their daily vitamin D requirements had an increased risk of Alzheimer's and dementia in old age 61. According to a 2015 meta-analysis, the risk of Alzheimer's is increased by 21% when the vitamin D level [25-hydroxyvitamin D, abbreviated as 25(OH)D] falls below <50 nmol/L 62. Similar results exist for the risk of dementia according to the analysis.

In a study involving 650 teenagers, it was found that a deficiency in vitamin D can also lead to obesity 63. Thus, research from 2010 shows a significant inverse correlation between the 25-hydroxyvitamin D level and all measurements of obesity, including BMI, waist circumference, total fat mass, body fat percentage, visceral fat tissue, and abdominal fat tissue 64.

In addition, studies suggest that a vitamin D deficiency increases the likelihood of cancer, such as bladder cancer. 65 66 67. Additionally, there is a significant increase in mortality and morbidity rate. 68 69.

Due to increased susceptibility to respiratory infections, a deficiency also poses a higher risk for pneumonia. 70.

A meta-analysis from 2015 with 5,183 subjects shows that vitamin D deficiency increases the risk of developing anemia. 71.

Scientific studies suggest that vitamin D deficiency is also a risk factor for autoimmune diseases such as multiple sclerosis (a chronic inflammatory disease of the central nervous system), rheumatoid arthritis, and inflammatory bowel disease. 72 73 74 75.

Recognizing and Detecting Vitamin D Deficiency

The best way to detect a deficiency is by measuring the storage form of vitamin D in the blood 76 77. The storage form is 25-hydroxyvitamin D, abbreviated as 25(OH)D. Vitamin D kits are available in online stores. Blood is drawn from the finger and sent to a laboratory for analysis, with results being returned (costing approximately 30 to 40 euros). Measurement can also be done by a general practitioner (costing around 40 to 50 euros).

The blood levels are reported either as nanograms per milliliter (ng/ml) or nanomoles per liter (nmol/l) 78 79:

ConditionBlood Level for 25(OH)D
Ideal 40 - 70 ng/ml (100 - 175 nmol/l)
Sufficient > 20 ng/ml (> 50 nmol/l)
Insufficient < 20 ng/ml
Deficient < 12 ng/ml (< 30 nmol/l)

Vitamin D levels of 20 ng/ml to 40 ng/ml are associated with maximum health benefits 80 81 82. Levels of 20 ng/ml (50 nmol/l) are sufficient to suppress the secretion of parathyroid hormone (which increases blood calcium levels) and prevent the release of calcium from the bones 83. Other scientists consider vitamin D insufficiency to be present at levels of 21 to 29 ng/ml, which is associated with impaired bodily functions 84 85. Optimal serum levels of 25-hydroxyvitamin D [25(OH)D] are above 32 ng/ml (80 nmol/l) 86.

Treatment for Vitamin D Deficiency

If a vitamin D deficiency is detected, the existing symptoms should be discussed with a doctor. The focus is on determining the exact cause so that the symptoms do not recur shortly after. During this conversation, the next steps for treating the deficiency can be initiated. Treatment methods may include the administration of vitamin D supplements, exposure to artificial UVB light, and increased sunlight exposure 87.

To quickly correct a vitamin D deficiency, treatment with dietary supplements can be done over 8 weeks. In this case, a dose of 50,000 IU of vitamin D2 is administered once a week, often resulting in 25(OH)D concentrations of ≈75 nmol/l (30 ng/ml) 88.

The following treatment options are commonly practiced to address vitamin D deficiency using dietary supplements 89:

Vitamin D level = 25(OH)DMeasure
Mild deficiency:
10-19 ng/ml (25-47.5 nmol/l)
25 to 50 µg (1,000 to 2,000 IU) of cholecalciferol (Vitamin D3) daily
Moderate to severe deficiency:
< 9 ng/ml (22.5 nmol/l)
75 to 125 µg (1,000 to 2,000 IU) of cholecalciferol daily for at least 6 to 12 weeks
1,250 µg (50,000 IU) of ergocalciferol once a month for 3 to 6 months
Severe deficiency:
< 5 ng/ml (15 nmol/l)
1,250 µg (50,000 IU) of ergocalciferol once weekly for 4 weeks, then once a month

Conversion: 1 µg = 40 IU; 1 nmol/l = 0.4 ng/ml; 1 ng/ml = 2.5 nmol/l

In more severe cases, which may have led to lower bone density, therapy needs to be initiated. Often, vitamin D supplements with calcium are administered in such cases. 90. We generally advise against self-treatment. Measures should always be taken in consultation with a doctor.

Preventive Measures

In the summer, it is especially important to go outside and soak up the sunlight. This not only promotes the production of vitamin D but also boosts happiness. Depending on skin type, sunbathing without sunscreen for a few minutes should be considered since creams block the UVB rays needed for vitamin D synthesis. A rule of thumb is to expose yourself to sunlight that lasts approximately 50% as long as it takes to get a mild sunburn (slightly pink skin after 24 hours) 91. Afterwards, protect yourself from sunlight.

In the winter months, the body can draw on the Vitamin D reserves accumulated during the summer months for some time. Nevertheless, it is essential to ensure an adequate intake of foods rich in Vitamin D during the cold season. 92. Additionally, depending on the measured Vitamin D levels, supplementation may be advisable (especially for vegans).

Exposure of the body to specific UVB lamps is also suitable for preventing deficiency 93.

It is recommended to have 25-hydroxyvitamin D levels checked for deficiency once a year 94.